The present invention relates in general to the design of spin-on fluid filters and the filter-to-filter head interface. More specifically the present invention relates to the specific sequence of thread and seal (inner and outer) engagements between the filter and the filter head in order to facilitate easier installation.
A related embodiment of the present invention includes a fluid filter with a nutplate having an internally threaded aperture which is larger, compared to earlier designs, in order to provide a reduced moment arm. Included in this related embodiment are novel inner and outer seals which provide improved performance characteristics.
The installation of spin-on filters typically calls for one-half to one turn installation following outer-gasket first contact. This point of first contact is difficult to determine if the fluid filter is designed with a positive inner seal to avoid bypass flow during use. The difficulty arises because the inner seal typically makes contact before the outer seal, causing a resistance to turning of the filter, far greater than the friction of gasket first contact. Also, due to the wide tolerance stack up of the filter assembly, the inner seal must make contact very early in the assembly such that it also makes contact before the first thread is engaged, thereby making it difficult to prevent cross threading. Removal of the fluid filter is also difficult because the end user must break loose the outer seal and the inner seal at the same time. Separating this breakaway point for each seal reduces the difficulty of filter removal.
The basic concept of a spin-on filter requires that a fully assembled filter be a stand alone unit, ready to use, only altered by gasket compression and filling of liquid as it is installed for use. If this concept is varied by recognizing that the filter is always used in conjunction with a filter head, then it is possible to allow the head to become part of the inner filter assembly during installation. Recognition of this allows several improvements to the typical spin-on filter assembly, as provided by the present invention. A typical spin-on filter has a spring in the bottom of the filter to press the filtering element tightly against the bottom of the nutplate. This spring takes up tolerance variations in the total assembly. Better quality filters are equipped with an inner seal to ensure that clean and dirty fluids are kept separate. This is typically a radial seal. Tolerance stack up of the distance between the lip of the inner seal and the top of the outer seal can be considerable. Adding this to the tolerance of the filter head between the bottom of the outer gasket and the inner seal surface requires that the protrusion on the head for the inner radial seal be longer than nominally required by the design to ensure that the radial inner seal is fully engaged under the worst tolerance conditions. Also, the radial inner seal requires much greater radial compression than is nominally required to allow for the considerable lack of concentricity control inherent in the construction of spin-on filters. This tight radial compression coupled with the longer protrusion of the filter head inner radial seal surface challenges the filter designer to provide for the thread engagement before the considerable torque drag of the inner seal mechanism comes into play. Height requirements of the filter assembly usually compromise this situation.
However, if one recognizes that the filter element is already floating in the assembly on a spring, this can be used to an advantage. A protrusion on the filter head can be designed to push the element down during installation, separating it from the nutplate and the rest of the nutplate and shell assembly. This protrusion can either press on the center of the top of the inner radial seal where it rests on the element top plate, just outside the inner radial seal protrusion on the head, or near the outer edge of the inner radial seal where it rests on the element top plate, just inside the thread minor diameter on the nutplate. This approach removes all concentricity issues as the element is now free to float and align itself to the inner radial seal. This means that the inner radial seal will not require as much radial compression. The tolerance of the lip of the inner radial seal need now be controlled by only one dimension, the level of the top of the inner radial seal to the edge of the lip. The radial seal portion of the inner radial seal protrusion on the head can now be located and toleranced by one dimension, the distance from the surface that bears on the inner radial seal to the end of the protrusion. This allows the protrusion to be much shorter.
By means of the present invention, once the head surface that bears on the inner radial seal is in full contact, the radial inner seal is fully engaged. At this point, the filtering element becomes part of the filter head and the rest of the filter nutplate and shell assembly can rotate around it, using the spring in the bottom of the filter as a thrust bearing. If desired, a separate thrust bearing can be added beneath the spring to ensure the lowest possible friction. From this point on, the radial flow area of the filter assembly can be set by the relationship of the head surface that bears on the inner radial seal to the rest of the head. It thus becomes much easier for the end user to feel outer seal first contact. More accurate outer seal compression ensures a better seal and discourages over tightening. Over tightening of the outer seal may lead to greater difficulty when removing the filter from the filter head, later.
When the end user removes the filter, the increased accuracy of the installation, coupled with the need to only break the outer seal loose, makes the initial turning of the fluid filter much easier. The threads on the nutplate act as a screw press to pull the inner seal out of the filtering element. Since the inner radial seal does not require as much radial compression, it is easier to break this seal loose after use.
According to the present invention, existing filter designs can be improved upon by getting away from the concept that the filter assembly must be "ready to use" as a stand alone unit. This of course is never the actual situation since the filter must always be installed on a filter head before it can be used. The present invention allows the filter head to adjust the assembly during installation. Thread alignment is done first. Thread engagement is made next. The inner seal is next fully engaged. Once fully engaged, the inner seal no longer spins and the filter shell spins around the element and the inner seal portion of the filter head, using the spring in the bottom of the filter as a thrust bearing. The filter head next opens the flow area of the filter by pushing the filter element down against the support spring. Finally, with only the friction of the threads and the support spring to resist turning, the point of outer seal first contact can be easily determined, allowing for more accurate compression of the outer seal.
Over the years, a variety of fluid filters have been designed and the following list is believed to provide a representative sampling of earlier design efforts which may be of interest with regard to the present invention.
______________________________________ PATENT NO. PATENTEE ISSUE DATE ______________________________________ 4,841,628 Nagle Jun. 27, 1989 4,839,037 Bertelsen et al. Jun. 13, 1989 4,855,047 Firth Aug. 8, 1989 5,118,417 Deibel Jun. 2, 1992 5,548,893 Koelfgen Aug. 27, 1996 4,992,166 Lowsky et al. Feb. 12, 1991 5,171,430 Beach et al. Dec. 15, 1992 5,395,518 Gulsvig Mar. 7, 1995 4,052,307 Humbert, Jr. Oct. 4, 1977 1,033,858 Adams Jul. 30, 1912 2,646,886 Le Clair Jul. 28, 1953 2,743,019 Kovacs Apr. 24, 1956 3,859,216 Sisson et al. Jan. 7, 1975 5,300,223 Wright Apr. 5, 1994 5,445,734 Chen Aug. 29, 1995 1,647,799 Hammer Nov. 1, 1927 ______________________________________
While a variety of different designs have been conceived of over the years, the present invention remains novel and unobvious.